The present invention relates to a driving mechanism for a member of timepiece moving intermittently, especially of a date or days indicator which moves one step each 24 hours, and comprises a driving member which rotates continuously and which is provided with means acting once each revolution, at least indirectly on a driven member, i.e. the intermittently moving member.
Mechanisms of this type, especially date mechanisms of the so-called dragging type (namely those in which the intermittently driven member rotates at least for a portion of each of its steps at the speed of the driving member) have the advantage of having good efficiency in that the energy which is transmitted by the gearing of the movement to the mechanism driving the intermittently moving member is very close to that required for driving this member. Consequently, there is less loss of energy as compared to mechanisms of the so-called instantaneous type in which the member moving intermittently effects its movements in sudden steps, thereby giving rise to a loss of energy due to the shock each time the intermittent member moves.
However, in the case of the mechanisms of the dragging type, if the efficiency is good, the distribution of the consumption of energy is bad since the driving member travels through a large portion of its stroke without furnishing any driving energy to the member moving intermittently and must furnish energy for this purpose only during a short portion of its stroke during which it is necessary to apply a relatively high torque to this member. Consequently, the movement has to be arranged in such a way as to be able to furnish such high peaks of torque.
In mechanisms of the instantaneous type, this inconvenience does not exist because the energy is generally accumulated by a spring during the entire revolution of the driving member, this stored energy being suddenly released when the intermittently moving member is driven.
The purpose of the present invention is to better distribute the consumption of energy in the case of the mechanisms of the dragging type, thereby permitting reduction in the maximum torque which has to be furnished to the driving mechanism of the intermittently moving member.